Promoted multi-metal catalyst

ABSTRACT

A catalyst comprising an In promoted mixed metal oxide is useful for the vapor phase oxidation of an alkane, or a mixture of an alkane and an alkene, to an unsaturated carboxylic acid and for the vapor phase ammoxidation of an alkane, or a mixture of an alkane and an alkene, to an unsaturated nitrile

This non-provisional application is a divisional of non-provisionalApplication No. 09/928,020, filed Aug. 10, 2001, benefit of which isclaimed under 35 USC 120, which in turn claims benefit under 35 USC119(e) of provisional Application No. 60/236,112, filed Sep. 28, 2000,priority benefit of which is also claimed for the present application,and provisional Application No. 60/283,245, filed Apr. 12, 2001,priority benefit of which is also claimed for the present application.

The present invention relates to an improved catalyst for the oxidationof alkanes, or a mixture of alkanes and alkenes, to their correspondingunsaturated carboxylic acids by vapor phase catalytic oxidation; to amethod of making the catalyst; and to a process for the vapor phasecatalytic oxidation of alkanes, or a mixture of alkanes and alkenes, totheir corresponding unsaturated carboxylic acids.

The present invention also relates to a method of producing unsaturatednitrites by subjecting alkanes, or a mixture of alkanes, and alkenes tovapor phase catalytic oxidation in the presence of ammonia.

Nitriles, such as acrylonitrile and methacrylonitrile, have beenindustrially produced as important intermediates for the preparation offibers, synthetic resins, synthetic rubbers, and the like. The mostpopular method for producing such nitrites is to subject an olefin suchas propene or isobutene to a catalytic reaction with ammonia and oxygenin the presence of a catalyst in a gaseous phase at a high temperature.Known catalysts for conducting this reaction include a Mo—Bi—P—Ocatalyst, a V—Sb—O catalyst, an Sb—U—V—Ni—O catalyst, a Sb—Sn—Ocatalyst, a V—Sb—W—P—O catalyst and a catalyst obtained by mechanicallymixing a V—Sb—W—O oxide and a Bi—Ce—Mo—W—O oxide. However, in view ofthe price difference between propane and propene or between isobutaneand isobutene, attention has been drawn to the development of a methodfor producing acrylonitrile or methacrylonitrile by an ammoxidationreaction wherein a lower alkane, such as propane or isobutane, is usedas a starting material, and it is catalytically reacted with ammonia andoxygen in a gaseous phase in the presence of a catalyst.

In particular, U.S. Pat. No. 5,281,745 discloses a method for producingan unsaturated nitrile comprising subjecting an alkane and ammonia inthe gaseous state to catalytic oxidation in the presence of a catalystwhich satisfies the conditions:

(1) the mixed metal oxide catalyst is represented by the empiricalformula

Mo_(a)V_(b)Te_(c)X_(x)O_(n)

wherein X is at least one element selected from the group consisting ofniobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron and cerium and, when a=1, b=0.01 to1.0, c=0.01 to 1.0, x=0.01 to 1.0 and n is a number such that the totalvalency of the metal elements is satisfied; and

(2) the catalyst has X-ray diffraction peaks at the following angles(±0.3°) of 2θ in its X-ray diffraction pattern: 22.1°, 28.2°, 36.2°,45.2° and 50.0°.

Similarly, Japanese Laid-Open Patent Application Publication No.6-228073 discloses a method of nitrile preparation comprising reactingan alkane in a gas phase contact reaction with ammonia in the presenceof a mixed metal oxide catalyst of the formula

W_(a)V_(b)Te_(c)X_(x)O_(n)

wherein X represents one or more elements selected from niobium,tantalum, titanium, aluminum, zirconium, chromium, manganese, iron,ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony,bismuth, indium and cerium and, when a=1, b=0.01 to 1.0, c=0.01 to 1.0,x=0.01 to 1.0 and n is determined by the oxide form of the elements.

U.S. Pat. No. 6,043,185 also discloses a catalyst useful in themanufacture of acrylonitrile or methacrylonitrile by the catalyticreaction in the vapor phase of a paraffin selected from propane andisobutane with molecular oxygen and ammonia by catalytic contact of thereactants in a reaction zone with a catalyst, wherein the catalyst hasthe empirical formula

Mo_(a)V_(b)Sb_(c)Ga_(d)X_(e)O_(x)

where X is one or more of As, Te, Se, Nb, Ta, W, Ti, Zr, Cr, Mn, Fe, Ru,Co, Rh, Ni, Pd, Pt, B, In, Ce, Re, Ir, Ge, Sn, Bi, Y, Pr, an alkalimetal and an alkaline earth metal; and when a=1, b=0.0 to 0.99, c=0.01to 0.9, d=0.01 to 0.5, e=0.0 to 1.0 and x is oxidation state of thecations present.

Unsaturated carboxylic acids such as acrylic acid and methacrylic acidare industrially important as starting materials for various syntheticresins, coating materials and plasticizers. Commercially, the currentprocess for acrylic acid manufacture involves a two-step catalyticoxidation reaction starting with a propene feed. In the first stage,propene is converted to acrolein over a modified bismuth molybdatecatalyst. In the second stage, acrolein product from the first stage isconverted to acrylic acid using a catalyst composed of mainly molybdenumand vanadium oxides. In most cases, the catalyst formulations areproprietary to the catalyst supplier, but, the technology is wellestablished. Moreover, there is an incentive to develop a single stepprocess to prepare the unsaturated acid from its corresponding alkene.Therefore, the prior art describes cases where complex metal oxidecatalysts are utilized for the preparation of unsaturated acid from acorresponding alkene in a single step.

European Published Patent Application No. 0 630 879 B1 discloses aprocess for producing an unsaturated aldehyde and a carboxylic acidwhich comprises subjecting propene, isobutene or tertiary butanol to gasphase catalytic oxidation with molecular oxygen in the presence of (i) acatalyst composite oxide represented by the formula

Mo_(a)Bi_(b)Fe_(c)A_(d)B_(e)C_(f)D_(g)O_(x)

wherein A represents Ni and/or Co, B represents at least one elementselected from Mn, Zn, Ca, Mg, Sn and Pb, C represents at least oneelement selected from P, B, As, Te, W, Sb and Si, and D represents atleast one element selected from K, Rb, Cs and Tl; and wherein, whena=12, 0<b≦10, 0≦c≦10, 1≦d≦10, 0≦e≦10, 0≦f≦20 and 0≦g≦2, and x has avalue dependent on the oxidation state of the other elements; and (ii) amolybdenum oxide which in itself is substantially inert to said gasphase catalytic oxidation to provide the corresponding unsaturatedaldehyde and unsaturated carboxylic acid.

Japanese Laid-Open Patent Application Publication No. 07-053448discloses the manufacture of acrylic acid by the gas-phase catalyticoxidation of propene in the presence of mixed metal oxides containingMo, V, Te, O and X wherein X is at least one of Nb, Ta, W, Ti, Al, Zr,Cr, Mn, Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B, In, Li, Na, K, Rb, Cs andCe.

Published International Application No. WO 00/09260 discloses a catalystfor selective oxidation of propene to acrylic acid and acroleincontaining a catalyst composition comprising the elements Mo, V, La, Pd,Nb and X in the following ratio:

Mo_(a)V_(b)La_(c)Pd_(d)Nb_(e)X_(f)

wherein X is Cu or Cr or a mixture thereof,

a is 1,

b is 0.01 to 0.9,

c is >0 to 0.2,

d is 0.0000001 to 0.2,

e is 0 to 0.2,

f is 0 to 0.2; and

wherein the numerical values of a, b, c, d, e and f represent therelative gram-atom ratios of the elements Mo, V, La, Pd, Nb and X,respectively, in the catalyst and the elements are present incombination with oxygen.

Commercial incentives also exist for producing acrylic acid using alower cost propane feed. Therefore, the prior art describes caseswherein a mixed metal oxide catalyst is used to convert propane toacrylic acid in one step.

U.S. Pat. No. 5,380,933 discloses a method for producing an unsaturatedcarboxylic acid comprising subjecting an alkane to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing amixed metal oxide comprising, as essential components, Mo, V, Te, O andX, wherein X is at least one element selected from the group consistingof niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium,manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium,platinum, antimony, bismuth, boron, indium and cerium; and wherein theproportions of the respective essential components, based on the totalamount of the essential components, exclusive of oxygen, satisfy thefollowing relationships:

0.25<r(Mo)<0.98, 0.003<r(V)<0.5, 0.003<r(Te)<0.5 and 0.003<r(X)<0.5,wherein r(Mo), r(V), r(Te) and r(X) are the molar fractions of Mo, V, Teand X, respectively, based on the total amount of the essentialcomponents exclusive of oxygen.

Published International Application No. WO 00/29106 discloses a catalystfor selective oxidation of propane to oxygenated products includingacrylic acid, acrolein and acetic acid, said catalyst system containinga catalyst composition comprising

Mo_(a)V_(b)Ga_(c)Pd_(d)Nb_(e)X_(f)

wherein X is at least one element selected from La, Te, Ge, Zn, Si, Inand W,

a is 1,

b is 0.01 to 0.9,

c is >0 to 0.2,

d is 0.0000001 to 0.2,

e is >0 to 0.2, and

f is 0.0 to 0.5; and

wherein the numerical values of a, b, c, d, e and f represent therelative gram-atom ratios of the elements Mo, V, Ga, Pd, Nb and X,respectively, in the catalyst and the elements are present incombination with oxygen.

Japanese Laid-Open Patent Application Publication No. 2000-037623discloses a method for producing an unsaturated carboxylic acidcomprising subjecting an alkane to a vapor phase catalytic oxidation inthe presence of a catalyst having the empirical formula

 MoV_(a)Nb_(b)X_(c)Z_(d)O_(n)

wherein X is at least one element selected from the group consisting ofTe and Sb, Z is at least one element selected from the group consistingof W, Cr, Ta, Ti, Zr, Hf, Mn, Re, Fe, Ru, Co, Rh, Ni, Pd, Pt, Ag, Zn, B,Al, Ga, In, Ge, Sn, Pb, P, Bi, Y, rare earth elements and alkaline earthelements, 0.1≦a≦1.0, 0.01≦b≦1.0, 0.01≦c≦1.0, 0≦d≦1.0 and n determined bythe oxidation states of the other elements.

Despite the above-noted attempts to provide new and improved catalystsfor the oxidation of alkanes to unsaturated carboxylic acids and for theammoxidation of alkanes to unsaturated nitrites, a need continues toexist for the provision of further improved catalysts.

By the present invention, there are provided improved catalysts whereinthe activity and selectivity are enhanced as compared to the basecatalyst and, hence, the overall yield of the desired reaction productis also enhanced.

Thus, in a first aspect, the present invention provides a catalystcomprising a promoted mixed metal oxide having the empirical formula

Mo_(a)V_(b)N_(c)X_(d)Z_(e)O_(f)

wherein

N is at least one element selected from the group consisting of Te, Sb,Sn, Ge and Bi,

X is at least one element selected from the group consisting of Nb, Ta,Ti, Al , Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs,Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu,La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu and Zn, and

Z is selected from the group consisting of In and Re; and wherein, whena=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, e=0.001 to 0.1 and fis dependent on the oxidation state of the other elements.

In a second aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane or a mixture of an alkane and an alkene to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing apromoted mixed metal oxide having the empirical formula

Mo_(a)V_(b)N_(c)X_(d)Z_(e)O_(f)

wherein

N is at least one element selected from the group consisting of Te, Sb,Sn, Ge and Bi,

X is at least one element selected from the group consisting of Nb, Ta,Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs,Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu,La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu and Zn, and

Z is selected from the group consisting of In and Re; and wherein, whena=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, e=0.001 to 0.1 and fis dependent on the oxidation state of the other elements.

In a third aspect, the present invention provides a process forproducing an unsaturated nitrile, which comprises subjecting an alkane,or a mixture of an alkane and an alkene, and ammonia to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containing apromoted mixed metal oxide having the empirical formula

Mo_(a)V_(b)N_(c)X_(d)Z_(e)O_(f)

wherein

N is at least one element selected from the group consisting of Te, Sb,Sn, Ge and Bi,

X is at least one element selected from the group consisting of Nb, Ta,Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs,Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu,La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu and Zn, and

Z is selected from the group consisting of In and Re; and wherein, whena=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, e 0.001 to 1.0 and fis dependent on the oxidation state of the other elements.

In a fourth aspect, the present invention provides a catalyst producedby the process comprising:

(1) admixing compounds of the elements Mo, V, N, X and Z and at leastone solvent to form an admixture, wherein

N is at least one element selected from the group consisting of Te, Sb,Sn Ge and Bi,

X is at least one element selected from the group consisting of Nb, Ta,Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs,Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu,La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu, and Zn,and

Z is selected from the group consisting of In and Re; and wherein theelements Mo, V, N, X and Z are present in such amounts that the atomicratio of Mo:V:N:X:Z is 1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0:0.001 to0.1;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor.

In a fifth aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane or a mixture of an alkane and an alkene to a vapor phasecatalytic oxidation reaction in the presence of the catalyst produced bythe process comprising:

(1) admixing compounds of the elements Mo, V, N, X and Z and at leastone solvent to form an admixture, wherein

N is at least one element selected from the group consisting of Te, Sb,Sn, Ge and Bi,

X is at least one element selected from the group consisting of Nb, Ta,Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs,Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu,La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu and Zn, and

Z is selected from the group consisting of In and Re; and

wherein the elements Mo, V, N, X and Z are present in such amounts thatthe atomic ratio of Mo:V:N:X:Z is 1:0.01 to 1.0:0.01 to 1.0:0.01 to1.0:0.001 to 0.1;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor.

In a sixth aspect, the present invention provides a process forproducing an unsaturated nitrile, which comprises subjecting an alkane,or a mixture of an alkane and an alkene, and ammonia to a vapor phasecatalytic oxidation reaction in the presence of the catalyst produced bythe process comprising:

(1) admixing compounds of the elements Mo, V, N, X and Z and at leastone solvent to form an admixture, wherein

N is at least one element selected from the group consisting of Te, Sb,Sn, Ge and Bi,

X is at lest one element selected from the group consisting of Nb, Ta,Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs,Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu,La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu and Zn, and

Z is selected from the group consisting of In and Re; and wherein theelements Mo, V, N, X and Z are present in such amounts that the atomicratio of Mo:V:N:X:Z is 1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0:0.001 to0.1;

(2) removing said at least one solvent from the admixture to obtain acatalyst precursor; and

(3) calcining said catalyst precursor.

The mixed metal oxide to be used as a catalyst component of the presentinvention has the empirical formula

Mo_(a)V_(b)N_(c)X_(d)Z_(e)O_(f)

wherein

N is at least one element selected from the group consisting of Te, Sb,Sn, Ge and Bi,

X is at least one element selected from the group consisting of Nb, Ta,Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs,Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu,La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu and Zn, and

Z is selected from the group consisting of In and Re; and wherein, whena=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0, e=0.001 to 0.1 and fis dependent on the oxidation state of the other elements.

Preferably, when a=1, b=0.1 to 0.5, c=0.05 to 0.5, d=0.01 to 0.5 ande=0.001 to 0.05. More preferably, when a=1, b=0.15 to 0.45, c=0.05 to0.45, d=0.01 to 0.1 and e=0.001 to 0.01. The value of f, i.e. the amountof oxygen present, is dependent on the oxidation state of the otherelements in the catalyst. However, f is typically in the range of from 3to 4.7.

The improved mixed metal oxide can be prepared in the following manner.

In a first step a slurry or solution may be formed by admixing metalcompounds, preferably at least one of which contains oxygen, and atleast one solvent in appropriate amounts to form the slurry or solution.Generally, the metal compounds contain elements Mo, V, N, X, Z and O, aspreviously defined.

Suitable solvents include water; alcohols including, but not limited to,methanol, ethanol, propanol, and diols, etc.; as well as other polarsolvents known in the art. Generally, water is preferred. The water isany water suitable for use in chemical syntheses including, withoutlimitation, distilled water and de-ionized water. The amount of waterpresent is preferably an amount sufficient to keep the elementssubstantially in solution long enough to avoid or minimize compositionaland/or phase segregation during the preparation steps. Accordingly, theamount of water will vary according to the amounts and solubilities ofthe materials combined.

For example, when a mixed metal oxide of the formulaMo_(a)V_(b)Te_(c)Nb_(d)In_(e)O_(f) wherein the element N is Te and theelement X is Nb, is to be prepared, an aqueous solution of niobiumoxalate may be added to an aqueous solution or slurry of ammoniumheptamolybdate, ammonium metavanadate, telluric acid and indium nitrate,so that the atomic ratio of the respective metal elements would be inthe prescribed proportions.

Once the aqueous slurry or solution is formed, the water is removed byany suitable method, known in the art, to form a catalyst precursor.Such methods include, without limitation, vacuum drying, freeze drying,spray drying, rotary evaporation and air drying. Vacuum drying isgenerally performed at pressures ranging from 10 mmHg to 500 mmHg.Freeze drying typically entails freezing the slurry or solution, using ,for instance, liquid nitrogen, and drying the frozen slurry or solutionunder vacuum. Spray drying is generally performed under an inertatmosphere such as nitrogen or argon, with an inlet temperature rangingfrom 125° C. to 200° C. and an outlet temperature ranging from 75° C. to150° C. Rotary evaporation is generally performed at a bath temperatureof from 25° C. to 90° C. and at a pressure of from 10 mmHg to 760 mmHg,preferably at a bath temperature of from 40° to 90° C. and at a pressureof from 10 mmHg to 350 mmHg, more preferably at a bath temperature offrom 40° C. to 60° C. and at a pressure of from 10 mmHg to 40 mmHg. Airdrying may be effected at temperatures ranging from 25° C. to 90° C.Rotary evaporation is generally utilized.

Once obtained, the catalyst precursor is calcined. The calcination maybe conducted in an oxidizing atmosphere, e.g., in an oxygen-containingatmosphere or in a non-oxidizing atmosphere, i.e. in the substantialabsence of oxygen, e.g., in an inert atmosphere or in vacuo. The inertatmosphere may be any material which is substantially inert, i.e., doesnot react or interact with, the catalyst precursor. Suitable examplesinclude, without limitation, nitrogen, argon, xenon, helium or mixturesthereof. Typically, the inert atmosphere is argon or nitrogen. The inertatmosphere may flow over the surface of the catalyst precursor or maynot flow thereover (a static environment). When the inert atmospheredoes flow over the surface of the catalyst precursor, the flow rate canvary over a wide range, e.g., at a space velocity of from 1 to 500 hr⁻¹.

The calcination is usually performed at a temperature of from 350° C. to850° C., preferably from 400° C. to 700° C., more preferably from 500°C. to 640° C. The calcination is performed for an amount of timesuitable to form the aforementioned catalyst. Typically, the calcinationis performed for from 0.5 to 30 hours, preferably from 1 to 25 hours,more preferably for from 1 to 15 hours, to obtain the desired promotedmixed metal oxide.

In a preferred mode of operation, the catalyst precursor is calcined intwo stages. In the first stage, the catalyst precursor is calcined in anoxidizing environment (e.g. air) at a temperature of from 200° C. to400° C., preferably from 275° C. to 325° C. for from 15 minute 8 hours,preferably for from 1 to 3 hours. In the second stage, the material fromthe first stage is calcined in a non-oxidizing environment (e.g., aninert atmosphere) at a temperature of from 500° C. to 750° C.,preferably for from 550° C. to 650° C., for 15 minutes to 8 hours,preferably for from 1 to 3 hours. Optionally, a reducing gas, such as,for example, ammonia or hydrogen, may be added during the second stagecalcination.

In a particularly preferred mode of operation, the catalyst precursor inthe first stage is placed in the desired oxidizing atmosphere at roomtemperature and then raised to the first stage calcination temperatureand held there for the desired first stage calcination time. Theatmosphere is then replaced with the desired non-oxidizing atmospherefor the second stage calcination, the temperature is raised to thedesired second stage calcination temperature and held there for thedesired second stage calcination time.

Although any type of heating mechanism, e.g., a furnace, may be utilizedduring the calcination, it is preferred to conduct the calcination undera flow of the designated gaseous environment. Therefore, it isadvantageous to conduct the calcination in a bed with continuous flow ofthe desired gas(es) through the bed of solid catalyst precursorparticles.

With calcination, a catalyst is formed having the formulaMo_(a)V_(b)N_(c)X_(d)Z_(e)O_(f) wherein Mo, V, N, X, Z, O, a, b, c, d, eand f are as previously defined.

The starting materials for the above promoted mixed metal oxide are notlimited to those described above. A wide range of materials including,for example, oxides halides or oxyhalides, alkoxides, acetylacetonates,and organometallic compounds may be used. For example, ammoniumheptamolybdate may be utilized for the source of molybdenum in thecatalyst. However, compounds such as MoO₃, MoO₂, MoCl₅, MoOCl₄,Mo(OC₂H₅)₅, molybdenum acetylacetonate, phosphomolybdic acid andsilicomolybdic acid may also be utilized instead of ammoniumheptamolybdate. Similarly, ammonium metavanadate may be utilized for thesource of vanadium in the catalyst. However, compounds such as V₂O₅,V₂O₃, VOCl₃, VCl₄, VO(OC₂H₅)₃, vanadium acetylacetonate and vanadylacetylacetonate may also be utilized instead of ammonium metavanadate.The tellurium source may include telluric acid, TeCl₄, Te(OC₂H₅)₅,Te(OCH(CH₃)₂)₄ and TeO₂. The niobium source may include ammonium niobiumoxalate, Nb₂O₅, NbCl₅, niobic acid or Nb(OC₂H₅)₅ as well as the moreconventional niobium oxalate. The indium source may be In₂O₃, InCl,InCl₃, In(OH)₃, indium acetate, indium acetylacetonate or indiumisopropoxide, as well as In(NO₃)₃. The rhenium source may be ammoniumperrhenate, rhenium carbonyl, rhenium chloride, rhenium fluoride,rhenium oxide, rhenium pentacarbonyl bromide, rhenium pentacarbonylchloride and rhenium sulfide.

A mixed metal oxide, thus obtained, exhibits excellent catalyticactivities by itself. However, the promoted mixed metal oxide may beconverted to a catalyst having higher activities by grinding.

There is no particular restriction as to the grinding method, andconventional methods may be employed. As a dry grinding method, a methodof using a gas stream grinder may, for example, be mentioned whereincoarse particles are permitted to collide with one another in a highspeed gas stream for grinding. The grinding may be conducted not onlymechanically but also by using a mortar or the like in the case of asmall scale operation.

As a wet grinding method wherein grinding is conducted in a wet state byadding water or an organic solvent to the above mixed metal oxide, aconventional method of using a rotary cylinder-type medium mill or amedium-stirring type mill, may be mentioned. The rotary cylinder-typemedium mill is a wet mill of the type wherein a container for the objectto be ground is rotated, and it includes, for example, a ball mill and arod mill. The medium-stirring type mill is a wet mill of the typewherein the object to be ground, contained in a container is stirred bya stirring apparatus, and it includes, for example, a rotary screw typemill, and a rotary disc type mill.

The conditions for grinding may suitably be set to meet the nature ofthe above-mentioned promoted mixed metal oxide, the viscosity, theconcentration, etc. of the solvent used in the case of wet grinding, orthe optimum conditions of the grinding apparatus. However, the grindingmay be conducted until the average particle size of the ground catalystprecursor is at most 20 μm. Improvement in the catalytic performance mayoccur due to such grinding.

Further, in some cases, it is possible to further improve the catalyticactivities by further adding a solvent to the ground catalyst precursorto form a solution or slurry, followed by drying again. There is noparticular restriction as to the concentration of the solution orslurry, and it is usual to adjust the solution or slurry so that thetotal amount of the starting material compounds for the ground catalystprecursor is from 10 to 60 wt %. Then, this solution or slurry is driedby a method such as spray drying, freeze drying, evaporation to drynessor vacuum drying, preferably by the spray drying method. Further,similar drying may be conducted also in the case where wet grinding isconducted.

The oxide obtained by the above-mentioned method may be used as a finalcatalyst, but it may further be subjected to heat treatment usually at atemperature of from 200° to 700° C. for from 0.1 to 10 hours.

The mixed metal oxide thus obtained may be used by itself as a solidcatalyst, but may be formed into a catalyst together with a suitablecarrier such as silica, alumina, titania, aluminosilicate, diatomaceousearth, zeolite ZSM-5 or zirconia. Further, it may be molded into asuitable shape and particle size depending upon the scale or system ofthe reactor.

Alternatively, the metal components of the presently contemplatedcatalyst may be supported on materials such as alumina, silica,silica-alumina, zirconia, titania, etc. by conventional incipientwetness techniques. In one typical method, solutions containing themetals are contacted with the dry support such that the support iswetted; then, the resultant wetted material is dried, for example, at atemperature from room temperature to 200° C. followed by calcination asdescribed above. In another method, metal solutions are contacted withthe support, typically in volume ratios of greater than 3:1 (metalsolution:support), and the solution agitated such that the metal ionsare ion-exchanged onto the support. The metal-containing support is thendried and calcined as detailed above.

In its second aspect, the present invention provides a process forproducing an unsaturated carboxylic acid, which comprises subjecting analkane, or a mixture of an alkane and an alkene, to a vapor phasecatalytic oxidation reaction in the presence of a catalyst containingthe above promoted mixed metal oxide, to produce an unsaturatedcarboxylic acid.

In the production of such an unsaturated carboxylic acid, it ispreferred to employ a starting material gas which contains steam. Insuch a case, as a starting material gas to be supplied to the reactionsystem, a gas mixture comprising a steam-containing alkane, or asteam-containing mixture of alkane and alkene, and an oxygen-containinggas, is usually used. However, the steam-containing alkane, or thesteam-containing mixture of alkane and alkene, and the oxygen-containinggas may be alternately supplied to the reaction system. The steam to beemployed may be present in the form of steam gas in the reaction system,and the manner of its introduction is not particularly limited.

Further, as a diluting gas, an inert gas such as nitrogen, argon orhelium may be supplied. The molar ratio (alkane or mixture of alkane andalkene):(oxygen):(diluting gas): (H₂O) in the starting material gas ispreferably (1):(0.1 to 10):(0 to 20): (0.2 to 70), more preferably(1):(1 to 5.0):(0 to 10):(5 to 40).

When steam is supplied together with the alkane, or the mixture ofalkane and alkene, as starting material gas, the selectivity for anunsaturated carboxylic acid is distinctly improved, and the unsaturatedcarboxylic acid can be obtained from the alkane, or mixture of alkaneand alkene, in good yield simply by contacting in one stage. However,the conventional technique utilizes a diluting gas such as nitrogen,argon or helium for the purpose of diluting the starting material. Assuch a diluting gas, to adjust the space velocity, the oxygen partialpressure and the steam partial pressure, an inert gas such as nitrogen,argon or helium may be used together with the steam.

As the starting material alkane it is preferred to employ a C₃₋₈ alkane,particularly propane, isobutane or n-butane; more preferably, propane orisobutane; most preferably, propane. According to the present invention,from such an alkane, an unsaturated carboxylic acid such as anα,β-unsaturated carboxylic acid can be obtained in good yield. Forexample, when propane or isobutane is used as the starting materialalkane, acrylic acid or methacrylic acid will be obtained, respectively,in good yield.

In the present invention, as the starting material mixture of alkane andalkene, it is possible to employ a mixture of C₃₋₈alkane and C₃₋₈alkene,particularly propane and propene, isobutane and isobutene or n-butaneand n-butene. As the starting material mixture of alkane and alkene,propane and propene or isobutane and isobutene are more preferred. Mostpreferred is a mixture of propane and propene. According to the presentinvention, from such a mixture of an alkane and an alkene, anunsaturated carboxylic acid such as an α,β-unsaturated carboxylic acidcan be obtained in good yield. For example, when propane and propene orisobutane and isobutene are used as the starting material mixture ofalkane and alkene, acrylic acid or methacrylic acid will be obtained,respectively, in good yield. Preferably, in the mixture of alkane andalkene, the alkene is present in an amount of at least 0.5% by weight,more preferably at least 1.0% by weight to 95% by weight; mostpreferably, 3% by weight to 90% by weight.

As an alternative, an alkanol, such as isobutanol, which will dehydrateunder the reaction conditions to form its corresponding alkene, i.e.isobutene, may also be used as a feed to the present process or inconjunction with the previously mentioned feed streams.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the oxidation reaction of the presentinvention is not clearly understood, but the oxidation reaction iscarried out by oxygen atoms present in the above promoted mixed metaloxide or by molecular oxygen present in the feed gas. To incorporatemolecular oxygen into the feed gas, such molecular oxygen may be pureoxygen gas. However, it is usually more economical to use anoxygen-containing gas such as air, since purity is not particularlyrequired.

It is also possible to use only an alkane, or a mixture of alkane andalkene, substantially in the absence of molecular oxygen for the vaporphase catalytic reaction. In such a case, it is preferred to adopt amethod wherein a part of the catalyst is appropriately withdrawn fromthe reaction zone from time to time, then sent to an oxidationregenerator, regenerated and then returned to the reaction zone forreuse. As the regeneration method of the catalyst, a method may, forexample, be mentioned which comprises contacting an oxidative gas suchas oxygen, air or nitrogen monoxide with the catalyst in the regeneratorusually at a temperature of from 300° to 600° C.

The second aspect of the present invention will be described in furtherdetail with respect to a case where propane is used as the startingmaterial alkane and air is used as the oxygen source. The reactionsystem may be a fixed bed system or a fluidized bed system. However,since the reaction is an exothermic reaction, a fluidized bed system maypreferably be employed whereby it is easy to control the reactiontemperature. The proportion of air to be supplied to the reaction systemis important for the selectivity for the resulting acrylic acid, and itis usually at most 25 moles, preferably from 0.2 to 18 moles per mole ofpropane, whereby high selectivity for acrylic acid can be obtained. Thisreaction can be conducted usually under atmospheric pressure, but may beconducted under a slightly elevated pressure or slightly reducedpressure. With respect to other alkanes such as isobutane, or tomixtures of alkanes and alkenes such as propane and propene, thecomposition of the feed gas may be selected in accordance with theconditions for propane.

Typical reaction conditions for the oxidation of propane or isobutane toacrylic acid or methacrylic acid may be utilized in the practice of thepresent invention. The process may be practiced in a single pass mode(only fresh feed is fed to the reactor) or in a recycle mode (at least aportion of the reactor effluent is returned to the reactor). Generalconditions for the process of the present invention are as follows: thereaction temperature can vary from 200° C. to 700° C., but is usually inthe range of from 200° C. to 550° C., more preferably 250° C. to 480°C., most preferably 300° C. to 400° C.; the gas space velocity, SV, inthe vapor phase reactor is usually within a range of from 100 to 10,000hr⁻¹, preferably 300 to 6,000 hr⁻¹, more preferably 300 to 2,000 hr⁻¹;the average contact time with the catalyst can be from 0.01 to 10seconds or more, but is usually in the range of from 0.1 to 10 seconds,preferably from 2 to 6 seconds; the pressure in the reaction zoneusually ranges from 0 to 75 psig, but is preferably no more than 50psig. In a single pass mode process, it is preferred that the oxygen besupplied from an oxygen-containing gas such as air. The single pass modeprocess may also be practiced with oxygen addition. In the practice ofthe recycle mode process, oxygen gas by itself is the preferred sourceso as to avoid the build up of inert gases in the reaction zone.

Of course, in the oxidation reaction of the present invention, it isimportant that the hydrocarbon and oxygen concentrations in the feedgases be maintained at the appropriate levels to minimize or avoidentering a flammable regime within the reaction zone or especially atthe outlet of the reactor zone. Generally, it is preferred that theoutlet oxygen levels be low to both minimize after-burning and,particularly, in the recycle mode of operation, to minimize the amountof oxygen in the recycled gaseous effluent stream. In addition,operation of the reaction at a low temperature (below 450° C.) isextremely attractive because after-burning becomes less of a problemwhich enables the attainment of higher selectivity to the desiredproducts. The catalyst of the present invention operates moreefficiently at the lower temperature range set forth above,significantly reducing the formation of acetic acid and carbon oxides,and increasing selectivity to acrylic acid. As a diluting gas to adjustthe space velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium may be employed.

When the oxidation reaction of propane, and especially the oxidationreaction of propane and propene, is conducted by the method of thepresent invention, carbon monoxide, carbon dioxide, acetic acid, etc.may be produced as by-products, in addition to acrylic acid. Further, inthe method of the present invention, an unsaturated aldehyde maysometimes be formed depending upon the reaction conditions. For example,when propane is present in the starting material mixture, acrolein maybe formed; and when isobutane is present in the starting materialmixture, methacrolein may be formed. In such a case, such an unsaturatedaldehyde can be converted to the desired unsaturated carboxylic acid bysubjecting it again to the vapor phase catalytic oxidation with thepromoted mixed metal oxide-containing catalyst of the present inventionor by subjecting it to a vapor phase catalytic oxidation reaction with aconventional oxidation reaction catalyst for an unsaturated aldehyde.

In its third aspect, the method of the present invention comprisessubjecting an alkane, or a mixture of an alkane and an alkene, to avapor phase catalytic oxidation reaction with ammonia in the presence ofa catalyst containing the above mixed metal oxide, to produce anunsaturated nitrile.

In the production of such an unsaturated nitrile, as the startingmaterial alkane, it is preferred to employ a C₃₋₈alkane such as propane,butane, isobutane, pentane, hexane and heptane. However, in view of theindustrial application of nitrites to be produced, it is preferred toemploy a lower alkane having 3 or 4 carbon atoms, particularly propaneand isobutane.

Similarly, as the starting material mixture of alkane and alkene, it ispossible to employ a mixture of C₃₋₈alkane and C₃₋₈alkene such aspropane and propene, butane and butene, isobutane and isobutene, pentaneand pentene, hexane and hexene, and heptane and heptene. However, inview of the industrial application of nitrites to be produced, it ispreferred to employ a mixture of a lower alkane having 3 or 4 carbonatoms and a lower alkene having 3 or 4 carbon atoms, particularlypropane and propene or isobutane and isobutene. Preferably, in themixture of alkane and alkene, the alkene is present in an amount of atleast 0.5% by weight, more preferably at least 1.0% by weight to 95% byweight, most preferably 3% by weight to 90% by weight.

The purity of the starting material alkane is not particularly limited,and an alkane containing a lower alkane such as methane or ethane, airor carbon dioxide, as impurities, may be used without any particularproblem. Further, the starting material alkane may be a mixture ofvarious alkanes. Similarly, the purity of the starting material mixtureof alkane and alkene is not particularly limited, and a mixture ofalkane and alkene containing a lower alkene such as ethene, a loweralkane such as methane or ethane, air or carbon dioxide, as impurities,may be used without any particular problem. Further, the startingmaterial mixture of alkane and alkene may be a mixture of variousalkanes and alkenes.

There is no limitation on the source of the alkene. It may be purchased,per se, or in admixture with an alkane and/or other impurities.Alternatively, it can be obtained as a by-product of alkane oxidation.Similarly, there is no limitation on the source of the alkane. It may bepurchased, per se, or in admixture with an alkene and/or otherimpurities. Moreover, the alkane, regardless of source, and the alkene,regardless of source, may be blended as desired.

The detailed mechanism of the ammoxidation reaction of this aspect ofthe present invention is not clearly understood. However, the oxidationreaction is conducted by the oxygen atoms present in the above promotedmixed metal oxide or by the molecular oxygen in the feed gas. Whenmolecular oxygen is incorporated in the feed gas, the oxygen may be pureoxygen gas. However, since high purity is not required, it is usuallyeconomical to use an oxygen-containing gas such as air.

As the feed gas, it is possible to use a gas mixture comprising analkane, or a mixture of an alkane and an alkene, ammonia and anoxygen-containing gas, However, a gas mixture comprising an alkane or amixture of an alkane and an alkene and ammonia, and an oxygen-containinggas may be supplied alternately.

When the gas phase catalytic reaction is conducted using an alkane, or amixture of an alkane and an alkene, and ammonia substantially free frommolecular oxygen, as the feed gas, it is advisable to employ a methodwherein a part of the catalyst is periodically withdrawn and sent to anoxidation regenerator for regeneration, and the regenerated catalyst isreturned to the reaction zone. As a method for regenerating thecatalyst, a method may be mentioned wherein an oxidizing gas such asoxygen, air or nitrogen monoxide is permitted to flow through thecatalyst in the regenerator usually at a temperature of from 300° C. to600° C.

The third aspect of the present invention will be described in furtherdetail with respect to a case where propane is used as the startingmaterial alkane and air is used as the oxygen source. The proportion ofair to be supplied for the reaction is important with respect to theselectivity for the resulting acrylonitrile. Namely, high selectivityfor acrylonitrile is obtained when air is supplied within a range of atmost 25 moles, particularly 1 to 15 moles, per mole of the propane. Theproportion of ammonia to be supplied for the reaction is preferablywithin a range of from 0.2 to 5 moles, particularly from 0.5 to 3 moles,per mole of propane. This reaction may usually be conducted underatmospheric pressure, but may be conducted under a slightly increasedpressure or a slightly reduced pressure. With respect to other alkanessuch as isobutane, or to mixtures of alkanes and alkenes such as propaneand propene, the composition of the feed gas may be selected inaccordance with the conditions for propane.

The process of the third aspect of the present invention may beconducted at a temperature of, for example, from 250° C. to 500° C. Morepreferably, the temperature is from 300° C. to 460° C. The gas spacevelocity, SV, in the gas phase reaction is usually within the range offrom 100 to 10,000 hr⁻¹, preferably from 300 to 6,000 hr⁻¹, morepreferably from 300 to 2,000 hr⁻¹. As a diluent gas, for adjusting thespace velocity and the oxygen partial pressure, an inert gas such asnitrogen, argon or helium can be employed. When ammoxidation of propaneis conducted by the method of the present invention, in addition toacrylonitrile, carbon monoxide, carbon dioxide, acetonitrile,hydrocyanic acid and acrolein may form as by-products.

EXAMPLES Comparative Example 1

In a flask containing 150 g of water, 34.00 g of ammonium heptamolybdatetetrahydrate (Aldrich Chemical Company), 6.69 g of ammoniummetavanadate(Alfa-Aesar) and 10.17 g of telluric acid (Aldrich ChemicalCompany) were dissolved upon heating to 80° C. After cooling to 20° C.,155.93 g of an aqueous solution of niobium oxalate (Reference MetalsCompany) containing 15.28 mmole/g of niobium and 3.76 g oxalic acid(Aldrich chemical Company) was mixed therewith to obtain a solution. Thewater of this solution was removed via a rotary evaporator at atemperature of 50° C. and a pressure of 28 mmHg to obtain the precursorsolid. The solid precursor were calcined in a quartz tube. (The quartztube was placed in an oven under an air atmosphere, the oven was heatedto 275° C. and held there for one hour; a flow of argon (100 cc/min)over the precursor material was then begun and the oven was heated to600° C. and held there for two hours.) The catalyst, thus obtained, waspressed in a mold and then broken and sieved to 10-20 mesh granules. 10g of these granules were packed into a stainless steel U-tube reactor(inside diameter: 1.1 cm) for the gas phase oxidation of propane. TheU-tube reactor was placed in a molten salt bath and fed with a mixtureof propane, air and steam having a feed ratio of propane/air/steam of1/15/14 and having a space velocity of 1200 hr⁻¹. The effluent of thereactor was condensed to separate a liquid phase and a gas phase. Thegas phase was analyzed by gas chromatography to determine the propaneconversion. The liquid phase was also analyzed by gas chromatography forthe yield of acrylic acid. The results (along with residence time andreactor temperature) are shown in Table 1.

TABLE 1 Residence Tem- Propane Acrylic Acid Acrylic Acid Time peratureConversion Selectivity Yield Catalyst (sec) (° C.) (%) (%) (%) Comp. 3350 49.0 62.3 30.5 Ex. 1 Comp. 3 360 59.8 60.5 36.2 Ex. 1 Comp. 3 36363.2 56.7 35.8 Ex. 1

Example 1

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.08)In_(0.01)O_(x) was prepared in thefollowing manner: 34.00 g of ammonium heptamolybdate tetrahydrate(Aldrich Chemical Company), 6.69 g of ammonium metavanadate(Alfa-Aesar), 10.07 g of telluric acid (Aldrich Chemical Company) and0.75 g of In(NO₃)₃*5H₂O (Aldrich Chemical Company) were dissolved inwater upon heating to 80° C. After cooling to 20° C., 155.93 g of anaqueous solution of niobium oxalate (Reference Metals Company)containing 15.28 mmole/g of niobium and 3.76 g oxalic acid (Aldrichchemical Company) was mixed therewith to obtain a solution. The water ofthis solution was removed via a rotary evaporator at a temperature of50° C. and a pressure of 28 mmHg to obtain the precursor solid. Thissolid precursor were calcined in a quartz tube. (The quartz tube wasplaced in an oven under an air atmosphere, the oven was heated to 275°C. and held there for one hour; a flow of argon (100 cc/min) over theprecursor material was then begun and the oven was heated to 600° C. andheld there for two hours.) The catalyst, thus obtained, was pressed in amold and then broken and sieved to 10-20 mesh granules. 10 g of thesegranules were packed into a stainless steel U-tube reactor (insidediameter: 1.1 cm) for the gas phase oxidation of propane. The U-tubereactor was placed in a molten salt bath and fed with a mixture ofpropane, air and steam having a feed ratio of propane/air/steam of1/15/14 and having a space velocity of 1200 hr⁻¹. The effluent of thereactor was condensed to separate a liquid phase and a gas phase. Thegas phase was analyzed by gas chromatography to determine the propaneconversion. The liquid phase was also analyzed by gas chromatography forthe yield of acrylic acid. The results (along with residence time andreactor temperature) are shown in Table 2.

TABLE 2 Residence Tem- Propane Acrylic Acid Acrylic Acid Time peratureConversion Selectivity Yield Catalyst (sec) (° C.) (%) (%) (%) Ex. 1 3340 65.0 63.9 41.6 Ex. 1 3 345 68.5 62.4 42.7 Ex. 1 3 346 71.8 59.9 43.0

Example 2

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.08)In_(0.050)O_(x) was prepared in thefollowing manner: 34.00 g of ammonium heptamolybdate tetrahydrate(Aldrich Chemical Company), 6.69 g of ammonium metavanadate(Alfa-Aesar), 10.07 g of telluric acid (Aldrich Chemical Company) and0.373 g of In(NO₃)₃*5H₂O (Aldrich Chemical Company) were dissolved inwater upon heating to 80° C. After cooling to 20° C., 155.93 g of anaqueous solution of niobium oxalate (Reference Metals Company)containing 15.28 mmole/g of niobium and 3.76 g oxalic acid (Aldrichchemical Company) was mixed therewith to obtain a solution. The water ofthis solution was removed via a rotary evaporator at a temperature of50° C. and a pressure of 28 mmHg to obtain the precursor solid. Thissolid precursor were calcined in a quartz tube. (The quartz tube wasplaced in an oven under an air atmosphere, the oven was heated to 275°C. and held there for one hour; a flow of argon (100 cc/min) over theprecursor material was then begun and the oven was heated to 600° C. andheld there for two hours.) The catalyst, thus obtained, was pressed in amold and then broken and sieved to 10-20 mesh granules. 10 g of thesegranules were packed into a stainless steel U-tube reactor (insidediameter: 1.1 cm) for the gas phase oxidation of propane. The U-tubereactor was placed in a molten salt bath and fed with a mixture ofpropane, air and steam having a feed ratio of propane/air/steam of1/15/14 and having a space velocity of 1200 hr⁻¹. The effluent of thereactor was condensed to separate a liquid phase and a gas phase. Thegas phase was analyzed by gas chromatography to determine the propaneconversion. The liquid phase was also analyzed by gas chromatography forthe yield of acrylic acid. The results (along with residence time andreactor temperature) are shown in Table 3.

TABLE 3 Residence Tem- Propane Acrylic Acid Acrylic Acid Time peratureConversion Selectivity Yield Catalyst (sec) (° C.) (%) (%) (%) Ex. 2 6335 66.4 68.1 45.2 Ex. 2   4.5 342 67.4 62.0 41.8 Ex. 2 3 350 65.4 64.442.1 Ex. 2 3 352 68.3 64.2 43.9

Comparative Example 2

In a flask containing 215 g of water, 25.68 g of ammonium heptamolybdatetetrahydrate (Aldrich Chemical Company), 5.06 g of ammoniummetavanadate(Alfa-Aesar) and 7.68 g of telluric acid (Aldrich ChemicalCompany) were dissolved upon heating to 70° C. After cooling to 40° C.,122.94 g of an aqueous solution of niobium oxalate (H. C. Starck)containing 1.25% Nb to which 2.84 g of oxalic acid (Aldrich ChemicalCompany) had been added was mixed therewith to obtain a solution. Thewater of this solution was removed via a rotary evaporator at atemperature of 50° C. and a pressure of 28 mmHg to obtain 46 g of aprecursor solid. 23 g of this catalyst precursor solid was calcined in aquartz tube. (The quartz tube was placed in an oven with a 100 cc/minflow of air through the tube, the oven was then heated to 275° C. at 10°C./min and held there for one hour; then using a 100 cc/min flow ofargon through the tube, the oven was heated to 600° C. at 2° C./min andheld there for two hours.) The catalyst, thus obtained, was pressed in amold and then broken and sieved to 10-20 mesh granules. 10 g of thesegranules were packed into a stainless steel U-tube reactor (insidediameter: 1.1 cm) for the gas phase oxidation of propane. The U-tubereactor was placed in a molten salt bath and fed with a mixture ofpropane, air and steam having a feed ratio of propane/air/steam of1/15/14 and having a space velocity of 1200 hr⁻¹. The effluent of thereactor was condensed to separate a liquid phase and a gas phase. Thegas phase was analyzed by gas chromatography to determine the propaneconversion. The liquid phase was also analyzed by gas chromatography forthe yield of acrylic acid. The results (along with residence time andreactor temperature) are shown in Table 4.

Example 3

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.08)Re_(0.01)O_(x) was prepared in thefollowing manner: 12.93 g of ammonium heptamolybdate tetrahydrate(Aldrich Chemical Company), 2.55 g of ammonium metavanadate(Alfa-Aesar), 3.87 g of telluric acid (Aldrich Chemical Company) and0.20 g of ammonium perrhenate (Aldrich Chemical Company) were dissolvedin 115 g of water upon heating to 70° C. After cooling to 40° C., 67.37g of an aqueous solution of niobium oxalate (H. C. Starck) containing1.25% Nb to which 1.43 g of oxalic acid (Aldrich Chemical Company) hadbeen added was mixed therewith to obtain a solution. The water of thissolution was removed via a rotary evaporator at a temperature of 50° C.and a pressure of 28 mmHg to obtain 23 g of a precursor solid. Thiscatalyst precursor solid was calcined in a quartz tube. (The quartz tubewas placed in an oven with a 100 cc/min flow of air through the tube,the furnace was then heated to 275° C. at 10° C./min and held there forone hour; then using a 100 cc/min flow of argon through the tube, theoven was heated to 600° C. at 2° C./min and held there for two hours.)The catalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules. 10 g of these granules were packed into astainless steel U-tube reactor (inside diameter: 1.1 cm) for the gasphase oxidation of propane. The U-tube reactor was placed in a moltensalt bath and fed with a mixture of propane, air and steam having a feedratio of propane/air/steam of 1/15/14 and having a space velocity of1200 hr⁻¹. The effluent of the reactor was condensed to separate aliquid phase and a gas phase. The gas phase was analyzed by gaschromatography to determine the propane conversion. The liquid phase wasalso analyzed by gas chromatography for the yield of acrylic acid. Theresults (along with residence time and reactor temperature) are shown inTable 4.

Example 4

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.08)Re_(0.005)O_(x) was prepared in thefollowing manner: 12.93 g of ammonium heptamolybdate tetrahydrate(Aldrich Chemical Company), 2.55 g of ammonium metavanadate(Alfa-Aesar), 3.87 g of telluric acid (Aldrich Chemical Company) and0.10 g of ammonium perrhenate (Aldrich Chemical Company) were dissolvedin 115 g of water upon heating to 70° C. After cooling to 40° C., 67.37g of an aqueous solution of niobium oxalate (H. C. Starck) containing1.25% Nb to which 1.43 g of oxalic acid (Aldrich Chemical Company) hadbeen added was mixed therewith to obtain a solution. The water of thissolution was removed via a rotary evaporator at a temperature of 50° C.and a pressure of 28 mmHg to obtain 28 g of a precursor solid. Thiscatalyst precursor solid was calcined in a quartz tube. (The quartz tubewas placed in an oven with a 100 cc/min flow of air through the tube,the furnace was then heated to 275° C. at 10° C./min and held there forone hour; then using a 100 cc/min flow of argon through the tube, theoven was heated to 600° C. at 2° C./min and held there for two hours.)The catalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules. 10 g of these granules were packed into astainless steel U-tube reactor (inside diameter: 1.1 cm) for the gasphase oxidation of propane. The U-tube reactor was placed in a moltensalt bath and fed with a mixture of propane, air and steam having a feedratio of propane/air/steam of 1/15/14 and having a space velocity of1200 hr⁻¹. The effluent of the reactor was condensed to separate aliquid phase and a gas phase. The gas phase was analyzed by gaschromatography to determine the propane conversion. The liquid phase wasalso analyzed by gas chromatography for the yield of acrylic acid. Theresults (along with residence time and reactor temperature) are shown inTable 4.

Example 5

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.08)Re_(0.0025)O_(x) was prepared in thefollowing manner: 12.93 g of ammonium heptamolybdate tetrahydrate(Aldrich Chemical Company), 2.55 g of ammonium metavanadate(Alfa-Aesar), 3.87 g of telluric acid (Aldrich Chemical Company) and0.05 g of ammonium perrhenate (Aldrich Chemical Company) were dissolvedin 115 g of water upon heating to 70° C. After cooling to 40° C., ⁶7.37g of an aqueous solution of niobium oxalate (H. C. Starck) containing1.25% Nb to which 1.43 g of oxalic acid (Aldrich Chemical Company) hadbeen added was mixed therewith to obtain a solution. The water of thissolution was removed via a rotary evaporator at a temperature of 50° C.and a pressure of 28 mmHg to obtain 28 g of a precursor solid. Thiscatalyst precursor solid was calcined in a quartz tube. (The quartz tubewas placed in an oven with a 100 cc/min flow of argon through the tube,the furnace was then heated to 275° C. at 10° C./min and held there forone hour; then using a 100 cc/min flow of argon through the tube, theoven was heated to 600° C. at 2° C./min and held there for two hours.)The catalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules. 10 g of these granules were packed into astainless steel U-tube reactor (inside diameter: 1.1 cm) for the gasphase oxidation of propane. The U-tube reactor was placed in a moltensalt bath and fed with a mixture of propane, air and steam having a feedratio of propane/air/steam of 1/15/14 and having a space velocity of1200 hr⁻¹. The effluent of the reactor was condensed to separate aliquid phase and a gas phase. The gas phase was analyzed by gaschromatography to determine the propane conversion. The liquid phase wasalso analyzed by gas chromatography for the yield of acrylic acid. Theresults (along with residence time and reactor temperature) are shown inTable 4.

Example 6

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.08)Re_(0.02)O_(x) was prepared in thefollowing manner: 12.93 g of ammonium heptamolybdate tetrahydrate(Aldrich Chemical Company), 2.55 g of ammonium metavanadate(Alfa-Aesar), 3.87 g of telluric acid (Aldrich Chemical Company) and0.39 g of ammonium perrhenate (Aldrich Chemical Company) were dissolvedin 115 g of water upon heating to 70° C. After cooling to 40° C., 67.37g of an aqueous solution of niobium oxalate (H. C. Starck) containing1.25% Nb to which 1.43 g of oxalic acid (Aldrich Chemical Company) hadbeen added was mixed therewith to obtain a solution. The water of thissolution was removed via a rotary evaporator at a temperature of 50° C.and a pressure of 28 mmHg to obtain 28 g of a precursor solid. Thiscatalyst precursor solid was calcined in a quartz tube. (The quartz tubewas placed in an oven with a 100 cc/min flow of air through the tube,the furnace was then heated to 275° C. at 10° C./min and held there forone hour; then using a 100 cc/min flow of argon through the tube, theoven was heated to 600° C. at 2° C./min and held there for two hours.)The catalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules. 10 g of these granules were packed into astainless steel U-tube reactor (inside diameter: 1.1 cm) for the gasphase oxidation of propane. The U-tube reactor was placed in a moltensalt bath and fed with a mixture of propane, air and steam having a feedratio of propane/air/steam of 1/15/14 and having a space velocity of1200 hr⁻¹. The effluent of the reactor was condensed to separate aliquid phase and a gas phase. The gas phase was analyzed by gaschromatography to determine the propane conversion. The liquid phase wasalso analyzed by gas chromatography for the yield of acrylic acid. Theresults (along with residence time and reactor temperature) are shown inTable 4.

Example 7

A catalyst of nominal compositionMo_(1.0)V_(0.3)Te_(0.23)Nb_(0.08)Re_(0.04)O_(x) was prepared in thefollowing manner: 12.93 g of ammonium heptamolybdate tetrahydrate(Aldrich Chemical Company), 2.55 g of ammonium metavanadate(Alfa-Aesar), 3.87 g of telluric acid (Aldrich Chemical Company) and0.79 g of ammonium perrhenate (Aldrich Chemical Company) were dissolvedin 115 g of water upon heating to 70° C. After cooling to 40° C., 67.37g of an aqueous solution of niobium oxalate (H.C. Starck) containing1.25% Nb to which 1.43 g of oxalic acid (Aldrich Chemical Company) hadbeen added was mixed therewith to obtain a solution. The water of thissolution was removed via a rotary evaporator at a temperature of 50° C.and a pressure of 28 mmHg to obtain 28 g of a precursor solid. Thiscatalyst precursor solid was calcined in a quartz tube. (The quartz tubewas placed in an oven with a 100 cc/min flow of air through the tube,the furnace was then heated to 275° C. at 10° C./min and held there forone hour; then using a 100 cc/min flow of argon through the tube, theoven was heated to 600° C. at 2° C./min and held there for two hours.)The catalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules. 10 g of these granules were packed into astainless steel U-tube reactor (inside diameter: 1.1 cm) for the gasphase oxidation of propane. The U-tube reactor was placed in a moltensalt bath and fed with a mixture of propane, air and steam having a feedratio of propane/air/steam of 1/15/14 and having a space velocity of1200 hr⁻¹. The effluent of the reactor was condensed to separate aliquid phase and a gas phase. The gas phase was analyzed by gaschromatography to determine the propane conversion. The liquid phase wasalso analyzed by gas chromatography for the yield of acrylic acid. Theresults (along with residence time and reactor temperature) are shown inTable 4.

Example 8

A catalyst of nominal compositionMo₁₀V_(0.3)Te_(0.23)Nb_(0.08)Re_(0.06)O_(x) was prepared in thefollowing manner: 12.93 g of ammonium heptamolybdate tetrahydrate(Aldrich Chemical Company), 2.55 g of ammonium metavanadate(Alfa-Aesar), 3.87 g of telluric acid (Aldrich Chemical Company) and1.18 g of ammonium perrhenate (Aldrich Chemical Company) were dissolvedin 115 g of water upon heating to 70° C. After cooling to 40° C., ⁶7.37g of an aqueous solution of niobium oxalate (H. C. Starck) containing1.25% Nb to which 1.43 g of oxalic acid (Aldrich Chemical Company) hadbeen added was mixed therewith to obtain a solution. The water of thissolution was removed via a rotary evaporator at a temperature of 50° C.and a pressure of 28 mmHg to obtain 28 g of a precursor solid. Thiscatalyst precursor solid was calcined in a quartz tube. (The quartz tubewas placed in an oven with a 100 cc/min flow of air through the tube,the furnace was then heated to 275° C. at 10° C./min and held there forone hour; then using a 100 cc/min flow of argon through the tube, theoven was heated to 600° C. at 2° C./min and held there for two hours.)The catalyst, thus obtained, was pressed in a mold and then broken andsieved to 10-20 mesh granules. 10 g of these granules were packed into astainless steel U-tube reactor (inside diameter: 1.1 cm) for the gasphase oxidation of propane. The U-tube reactor was placed in a moltensalt bath and fed with a mixture of propane, air and steam having a feedratio of propane/air/steam of 1/15/14 and having a space velocity of1200 hr⁻¹. The effluent of the reactor was condensed to separate aliquid phase and a gas phase. The gas phase was analyzed by gaschromatography to determine the propane conversion. The liquid phase wasalso analyzed by gas chromatography for the yield of acrylic acid. Theresults (along with residence time and reactor temperature) are shown inTable 4.

TABLE 4 Residence Propane Acrylic Acid Time Temperature Conversion YieldCatalyst (sec) (° C.) (%) (%) Comp. Ex. 2 3 380 17 12 Ex. 3 3 380 36 18Ex. 4 3 380 39 20 Ex. 5 3 380 44 20 Ex. 6 3 380 25 15 Ex. 7 3 380 29 13Ex. 8 3 380 10 3

What is claimed is:
 1. A process for producing an unsaturated carboxylicacid, which comprises subjecting a C₃₋₈ alkane or a mixture of a C₃₋₈alkane and a C₃₋₈ alkene to a vapor phase catalytic oxidation reactionin the presence of a catalyst containing a promoted mixed metal oxidehaving the empirical formula Mo_(a)V_(b)N_(c)X_(d)Z_(c)O_(f) wherein Nis at least one element selected from the group consisting of Te, Sb,Sn, Ge and Bi, X is at least one element selected from the groupconsisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co. Rh, Ni, Pt B, As,Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy,Ho, Er, Tm, Yb, Lu, La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb,W, Ce, Cu and Zn, and Z is selected from the group consisting of In andRe; and wherein, when a=1,b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0,e=0.001 to 0.1 and f is dependent on the oxidation state of the otherelements.
 2. A process for producing an unsaturated nitrile, whichcomprises subjecting a C₃₋₈ alkane, or a mixture of a C₃₋₈ alkane and aC₃₋₈ alkene, and ammonia to a vapor phase catalytic oxidation reactionin the presence of a catalyst containing a promoted mixed metal oxidehaving the empirical formula Mo_(a)V_(b)N_(c)X_(d)Z_(e)O_(f) wherein Nis at least one element selected from the group consisting of Te, Sb,Sn, Ge and Bi, X is at least one element selected from the groupconsisting of Nb, Ta, Ti, Al, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As,Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Hf, Pb, Pm, Pn, Eu, Gd, Dy,Ho, Er, Tm, Yb, Lu, La, Sc, Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb,W, Ce, Cu and Zn, and Z is selected from the group consisting of In andRe; and wherein, when a=1, b=0.01 to 1.0, c=0.01 to 1.0, d=0.01 to 1.0,e=0.001 to 1.0 and f is dependent on the oxidation state of the otherelements.
 3. A process for producing an unsaturated carboxylic acid,which comprises subjecting a C₃₋₈ alkane or a mixture of a C₃₋₈ alkaneand a C₃₋₈ alkene to a vapor phase catalytic oxidation reaction in thepresence of the catalyst produced by the process comprising: (1)admixing compounds of the elements Mo, V, N, X and Z and at least onepolar solvent to form an admixture, wherein N is at least one elementselected from the group consisting of Te, Sb, Sn, Ge and Bi, X is atleast one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Ca, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs, Fr, Be,Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, La, Sc,Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu and Zn, and Z isselected from the group consisting of In and Re; and wherein theelements Mo, V, N, X and Z are present in such amounts that the atomicratio of Mo:V:N:X:Z is 1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0:0.0001 to0.1; (2) removing said at least one polar solvent from the admixture toobtain a catalyst precursor; and (3) calcining said catalyst precursor.4. A process for producing an unsaturated nitrile, which comprisessubjecting a C₃₋₈ alkane, or a mixture of a C₃₋₈ alkane and a C₃₋₈alkene, and ammonia to a vapor phase catalytic oxidation reaction in thepresence of the catalyst produced by the process comprising: (4)admixing compounds of the elements Mo, V, N, X and Z and at least onepolar solvent to form an admixture, wherein N is at least one elementselected from the group consisting of Te, Sb, Sn, Ge and Bi, X is atleast one element selected from the group consisting of Nb, Ta, Ti, Al,Zr, Cr, Mn, Fe, Ru, Co, Rh, Ni, Pt, B, As, Li, Na, K, Rb, Cs, Fr, Be,Mg, Ca, Sr, Ba, Hf, Pb, P, Pm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, La, Sc,Au, Ag, Pd, Ga, Pr, Re, Ir, Nd, Y, Sm, Tb, W, Ce, Cu and Zn, and Z isselected from the group consisting of In and Re; and wherein theelements Mo, V, N, X and Z are present in such amounts that the atomicratio of Mo: V:N:X:Z is 1:0.01 to 1.0:0.01 to 1.0:0.01 to 1.0:0.001 to0.1; (5) removing said at least one polar solvent from the admixture toobtain a catalyst precursor; and (6) calcining said catalyst precursor.